1. Field of the Invention
The present invention relates to compositions comprising a functionalized block copolymer crosslinked aluminum acetylacetonate. More particularly, the present invention relates to novel compositions comprising a maleated, hydrogenated tri-block copolymer crosslinked with aluminum acetylacetonate.
2. Background of the Related Art
Compositions based on block copolymers having poly-vinyl-aromatic blocks such as polystyrene, and polydiene blocks such as polybutadiene or polyisoprene, or hydrogenated polydiene blocks such as polyethylene/butylene have a broad utility in commercial applications. Extensive work has been done to crosslink these copolymer blocks to increase upper service temperature and solvent resistance Much of this work has been done to develop pressure sensitive adhesives (PSA) which may be applied as hot melts and subsequently crosslinked by exposure to ultraviolet light or electron beam radiation via a free radical reaction in the unsaturated polydiene blocks. Free radical chemistry has proven to be acceptable for crosslinking ethylenically unsaturated multi-block copolymers containing polydiene blocks, however, free radical chemistry is not desirable for crosslinking saturated block copolymers containing hydrogenated polydiene blocks.
Compositions based on block copolymers having poly-vinyl-aromatic blocks and hydrogenated polydiene blocks are physically crosslinked through the well known domain structure formed by association of the poly-vinyl-aromatic blocks. As a result, compositions based on these physically crosslinked block copolymers may be advantageously processed as solvent-free thermoplastic compositions or as high solids solutions.
One disadvantage associated with compositions based on physically crosslinked multi-block copolymers is that the uses of these compositions are severely limited. Uses of the compositions may include adhesives, sealants, modified asphalt, and oil gels, for example. The domain structure formed by association of the poly-vinyl-aromatic blocks looses integrity when the composition is heated above the glass transition temperature of the poly-vinyl-aromatic blocks. As a result, the upper service temperature of compositions based on these physically crosslinked multi-block copolymers are limited to less than about 100xc2x0 C. Furthermore, the domain structure formed by association of the poly-vinyl-aromatic blocks looses integrity when the poly-vinyl-aromatic blocks are plasticized with solvent or a compatible plasticizer. As a result, compositions based on physically crosslinked multi-block copolymers weaken in the presence of solvents. Also, an adhesive composition based on these block copolymers is not suitable for use with plasticized polyvinylchloride (PVC) substrates because plasticizers, such as dioctylphthalate (DOP), which are typically used to soften PVC migrate into the adhesive and weaken the adhesive severely.
Therefore, there has been a long felt but unresolved need for a PSA based on crosslinked block copolymers which provides an increase in upper service temperature and improved solvent resistance. There is also a need for a PSA which may be used with PVC plasticized with DOP as a film backing for tapes, labels, and decals. There is further a need for sealants which do not slump out of a joint at higher temperatures. There is still further a need for oil gels which can maintain their shape at higher temperatures. There is yet further a need for modified asphalts which have higher softening points.
In one embodiment, this invention provides a composition comprising a functionalized block copolymer crosslinked with acetylacetonate. The crosslinked block copolymer has improved solvent resistance and improved cohesive strength at high temperatures. The crosslinked block copolymer comprises preferably an acid functionalized, hydrogenated block copolymer having an ABA or similar structure wherein the A block comprises at least 80 wt % of a vinyl-aromatic hydrocarbon, preferably styrene, and wherein the B block comprises at least 80 wt % of a hydrogenated conjugated diene, preferably butadiene, isoprene, or a mixture thereof.
In another embodiment, this invention provides an adhesive, sealant, oil gel, asphalt composition, or wax composition comprising the acid functionalized, hydrogenated block copolymer.
The present invention generally provides functionalized, hydrogenated-block copolymers crosslinked with aluminum acetylacetonate (AlAcAc). The copolymers are typically prepared by grafting maleic anhydride (MA) onto the block copolymer in an extruder grafting process. The acid groups grafted onto the copolymer form a reactive site which is then useful in a crosslinking reaction with the AlAcAc. Pressure sensitive adhesives comprising the block copolymers crosslinked with AlAcAc surprisingly exhibit an increased upper service temperature and improved solvent resistance. The adhesives can also prevent shrinkage of a DOP plasticized PVC film decal upon aging. Oil gels, modified asphalt, and modified waxes comprising the block copolymers crosslinked with AlAcAc surprisingly exhibit a very high softening point. Sealants comprising the block copolymers crosslinked with AlAcAc surprisingly exhibit good slump resistance at high temperatures.
The block copolymers, prior to hydrogenation, have both ethylenic and/or aromatic unsaturation, and may be prepared by copolymerizing one or more olefins, particularly a diolefin, with one or more alkenyl aromatic hydrocarbon monomers. The copolymers may be prepared using anionic initiators or polymerization catalysts using bulk, solution, or emulsion techniques.
In general, when solution anionic techniques are used, conjugated diolefin polymers and copolymers of conjugated diolefins and alkenyl aromatic hydrocarbons are prepared by contacting the monomer or monomers to be polymerized simultaneously or sequentially with an anionic polymerization initiator such as a Group IA metal or its alkyl, amide, silanolate, napthalide, biphenyl or anthracenyl derivative. It is preferred to use an organoalkali metal such as a sodium or potassium compound, for example, in a suitable solvent at a temperature within the range from about xe2x88x92100xc2x0 C. to about 200xc2x0 C., preferably at a temperature within the range from about 0xc2x0 C. to about 100xc2x0 C.
Particularly effective anionic polymerization initiators are organolithium compounds having the general formula:
RLin,
wherein R is an aliphatic, cycloaliphatic, aromatic or alkyl-substituted aromatic hydrocarbon radical having from 1 to about 20 carbon atoms; and n is an integer of 1 to 4.
Conjugated diolefins useful in preparing the block copolymers include conjugated diolefins containing from 4 to about 8 carbon atoms such as 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene and the like. Mixtures of such conjugated dienes may also be used. The preferred conjugated diene is 1,3-butadiene.
Alkenyl aromatic hydrocarbons useful in preparing the block copolymers include vinyl aryl compounds such as styrene, various alkyl-substituted styrenes such as p-methylstyrene, p-tert-butylstyrene, and alpha-methylstyrene, alkoxy-substituted styrenes, vinyl naphthalene, alkyl-substituted vinyl naphthalenes, and the like. The preferred vinyl aromatic hydrocarbon is styrene.
Any of the inert hydrocarbon solvents known in the prior art to be useful in the preparation of such polymers may be used. In particular, suitable solvents may include straight- and branched-chain hydrocarbons such as pentane, hexane, heptane, octane and the like, as well as, alkyl-substituted derivatives thereof; cycloaliphatic hydrocarbons such as cyclopentane, cyclohexane, cycloheptane and the like, as well as, alkyl-substituted derivatives thereof; aromatic and alkyl-substituted aromatic hydrocarbons such as benzene, naphthalene, toluene, xylene, and the like; hydrogenated aromatic hydrocarbons such as tetralin decalin, and the like.
The polymers of this invention may be hydrogenated as disclosed in U.S. Pat. No. Reissue 27,145, which is herein incorporated by reference. The hydrogenation of these polymers and copolymers may be carried out by a variety of well established processes including hydrogenation in the presence of such catalysts as Raney Nickel, noble metals such as platinum and the like, soluble transition metal catalysts as in U.S. Pat. Nos. 3,113,986 and 4,226,952, which are incorporated herein by reference, and titanium catalysts as in U.S. Pat. No. 5,039,755, which is also incorporated herein by reference. Hydrogenation should reduce at least about 50 percent, preferably at least 70 percent, more preferably at least 90 percent, and most preferably at least 99 percent of the olefinic unsaturation originally present in the polydiene block. Hydrogenation can be selective in which case the olefinic unsaturation is reduced from the polydiene block while the aromatic unsaturation in the poly-vinyl-aromatic block remains essentially unhydrogenated. If desired, hydrogenation can be complete in which case both the olefinic unsaturation and the aromatic unsaturation are reduced.
Block copolymers of conjugated dienes and vinyl aromatic hydrocarbons include any of those which exhibit elastomeric properties at the temperatures of use. Therefore, the polydiene block should be largely amorphous and not contain excessive crystallinity which would interfere with flexibility. Butadiene, for example, the percent of 1,2-addition should preferably be greater than about 30 percent to avoid crystallinity after hydrogenation. Below about 30 percent 1,2-addition, crystallinity is too high, producing a polymer which is too stiff for use in adhesives which must perform at temperatures as low as about 0xc2x0 C.
Suitable block copolymers as a precursor to the functionalized, hydrogenated block copolymers may have varying structures containing various ratios of conjugated dienes to vinyl aromatic hydrocarbons including those containing up to about 60 percent by weight of vinyl aromatic hydrocarbon. Thus, multiblock copolymers may be utilized which are linear or radial, symmetric or asymmetric, and which have structures represented by the formulae, A-B, A-B-A, A-B-A-B, B-A-B, (AB)0,1,2, . . . -BA and the like wherein A is a polymer block of a vinyl aromatic hydrocarbon or a conjugated diene/vinyl aromatic hydrocarbon tapered copolymer block comprising at least 80 wt % of the vinyl/aromatic hydrocarbon and B is a polymer block of a conjugated or a conjugated diene/vinyl/aromatic tapered copolymer block comprising at least 80 wt % of the conjugated diene. Suitably, the A block or blocks compose 5 to 60, preferably 5 to 30, percent by weight of the copolymer. Such blocks suitably have a number average molecular weight of 2,000 to 115,000 to preferably of 4,000 to 60,000. Suitably, the B block or blocks have a number average molecular weight of 20,000 to 450,000. Preferably, the block copolymer is a tri-block having the A-B-A structure, more preferably an ABA block copolymer having polystyrene end blocks.
The block copolymers may be produced by any well known block polymerization or copolymerization procedures including the well known sequential addition of monomer techniques, incremental addition of monomer technique or coupling technique as illustrated in, for example, U.S. Pat. Nos. 3,251,905; 3,390,207; 3,598,887 and 4,219,627, which are incorporated herein by reference.
The acid functionalized block copolymer may be prepared by graft-reacting an acid moiety or its derivative onto the hydrogenated block copolymer via a free radically initiated reaction. Suitable monomers which may be grafted include unsaturated mono- and polycarboxylic acids and anhydrides containing from about 3 to about 10 carbons. Examples of such monomers are fumaric acid, itaconic acid, citraconic acid, acrylic acid, maleic anhdride, itaconic anhydride, and citraconic anhydride. The preferred grafting monomer is maleic anhydride. The grafted polymer will usually contain from 0.1 to 10, preferably 0.2 to 5 percent by weight of grafted monomer.
The grafting reaction can be carried out in solution or by melt-mixing the base block copolymer and the acid/anhydride monomer in the presence of a free radical initiator. Disclosures for such processes are found in U.S. Pat. Nos. 4,033,888; 4,077,893; and 4,670,173 for solution processes and in U.S. Pat. Nos. 4,427,828; 4,578,429; 4,628,072; and 4,657,971 for melt-mixing processes, all of which are incorporated herein by reference.
The above-described polymers may be readily prepared by the methods set forth above. However, suitable polymers are commercially available from any of the KRATON Polymer companies. Preferred block copolymers which are commercially available are KRATON(copyright) G1652, KRATON(copyright) G1657, KRATON(copyright) G1726, KRATON(copyright) FG1901 and KRATON(copyright) FG1924.
It is believed that the crosslinked compositions described herein have utility in a broad range of applications where the thermoset properties of these compositions are required. Examples include applications in adhesives, including pressure sensitive adhesives for tapes and labels, contact adhesives, laminating adhesives, and assembly adhesives, which have improved load bearing capacity at elevated temperatures, in sealants which have better slump resistance at elevated temperatures, in oil gels which maintain their integrity at higher temperatures, in blends with asphalt for roofing products and waterproofing membranes which can be used at higher temperatures without sagging on sloped surfaces, and in blends with wax for use in non-drip candles or in coatings which stay in place on sloped surfaces.
Compositions based on acid functionalized block copolymers crosslinked with AlAcAc may be mixed and applied as a solvent solution The multi-block copolymers may be dissolved in a solvent blend containing a major amount of a hydrocarbon solvent, such as toluene, and a minor amount of a polar solvent, such as a ketone, an ester, or an alcohol. The amount of polar solvent depends on the particular polar solvent chosen and the structure of the particular polymer used in the formulation. However, the amount of polar solvent used in the blend is usually between about 10 and about 50 percent by weight of the solvent blend.
Aluminum Acetylacetonate (AlAcAc) is a solid having a melting point of 194xc2x0 C., and is preferably dissolved in a hydrocarbon solvent such as toluene, for example. However, AlAcAc is preferably dissolved in a blend of solvents such as a blend of toluene and isopropyl acetate (iPAc). Preferably, from about 10% by weight to about 25% by weight of solid AlAcAc, more preferably at least 10% by weight, is dissolved in the blend of toluene and iPAc. The blend of toluene and iPAc preferably has at least a 50:50 weight percent ratio of toluene and iPAc, and more preferably a 75:25 weight percent ratio of toluene and iPAc.
The copolymer solution and AlAcAc solution are then mixed in correct proportions immediately before applying the composition. Aluminum acetylacetonate is present in a concentration from about 0.2 percent by weight to about 10 percent by weight of the block copolymer. The two components are preferably mixed just before application because the curing reaction between the acid functionalized block copolymer and AlAcAc takes place at room temperature. Alternatively, 2,4-pentanedione may be included as part of the solvent system to inhibit the curing reaction.
After the solution have been mixed and applied, the solvents are allowed to evaporate and the crosslinking reaction allowed to proceed. The crosslinking reaction begins when the solutions are mixed, but complete cure can take several hours to several weeks depending on cure conditions.
Alternatively, compositions based on acid functionalized block copolymers crosslinked with AlAcAc may be mixed and applied as a solvent free hot melt. Typically, all the components except AlAcAc are mixed using an appropriate mixer and then the AlAcAc is added just prior to application. Mixing temperatures should be high enough to prevent gellation during mixing, and after addition of the AlAcAc, the hot melt should not cool before application, otherwise the hot melt will gel. Typically, the hot melt is mixed in a high shear mixer for about 1 to 3 hours at from about 100 to about 200xc2x0 C. After a homogeneous blend is obtained, the AlAcAc is added and mixing is continued for at least about 10 minutes before the hot melt is applied.
Ingredients in addition to the polymer, crosslinker, and solvent may be used to prepare compositions having a proper combination of properties, such as adhesion, cohesion, durability, low cost, etc., for a particular application. Thus, suitable formulations may contain combinations of additives, resins, plasticizers, fillers, and stabilizers, for example.
Resins and plasticizers may be used in many adhesive, sealant, and coating formulations to impart adhesion and to develop the proper mechanical and viscoelastic properties. A particular resin or plasticizer may be more compatible thermodynamically with the A block or with the B block of the polymer. Resins compatible with the A block are referred to as endblock resins. Generally, endblock resins make the compositions stiffer. Resins compatible with the B block are referred to as midblock resins. Generally, midblock resins make the compositions tacky and therefore, are called tackifying resins. Plasticizers compatible with the B block are used to soften the composition. Plasticizers compatible with the A block are generally not used since they reduce the glass transition temperature (Tg) of the A block.
Resins are low molecular weight hydrocarbon polymers, generally having molecular weights between about 500 and 5,000. Although resins may be liquids, most are brittle solids, characterized by a ring and ball softening point as determined by ASTM method E28. Most commonly used resins have softening points between about 80 and 140xc2x0 C. Midblock resins are usually aliphatic, cycloaliphatic, or aromatic modified aliphatic polymers.
Midblock resins can be used in formulations up to about 70 percent by weight of the composition. Examples of typical midblock resins from Hercules, Inc, include PICCOTAC, HERCOTAC, REGALREZ, REGALITE, PICCOLYTE, and FORAL. PICCOTAC resins are aliphatic. HERCOTAC resins are aromatic modified aliphatic resins. REGALREZ and REGALITE resins are hydrogenated aromatics. PICCOLYTE resins are polyterpenes and FORAL resins are rosin esters.
Endblock resins are highly aromatic polymers, and may be used in formulations up to about 40 percent by weight of the composition. Examples of typical endblock resins from Hercules, Inc, include PICCO, ENDEX, KRISTALEX and PICCOTEX PICCO resins are made by polymerizing an aromatic stream. ENDEX, KRISTALEX and PICCOTEX are made from pure monomers such as styrene, alpha-methylstyrene, and vinyl toluene.
Midblock plasticizers can be liquid resins or synthetic oils like polybutenes, but the most common midblock plasticizers are rubber compounding oils. These low aromatic content oils are well known in the art and include both high saturates content oils and naphthenic oils. Preferred oils are naphthenic process oils like the SHELLFLEX oils from Shell and the highly saturated white mineral oils like the TUFFLO oils from Arco and the DRAKEOL oils from Penreco. In adhesives and sealants, oil may be used up to about 30 percent by weight. In oil gels, oil may be as much as about 95 percent by weight of the composition.
Asphalts useful in the present invention are selected on the basis of their compatibility with the polymer in order to prevent the polymer from phase separating from the mixture. Generally, preferred asphalts are straight run, unblown asphalts, especially those derived from naphthenic crudes. For soft products, an asphalt having a penetration of about 150 may be used. For harder products, asphalts having a penetration as low as about 10 may be used. Blown asphalts may be used but greater attention must be paid to compatibility between the polymer and the asphalt. Low levels of asphalt may be used as a formulating ingredient in adhesives and sealants. For products like waterproofing membranes and road crack sealants, asphalt may comprise up to 95 percent by weight of the composition.
Useful waxes may include petroleum waxes, both paraffin and microcrystalline, such as the SHELLWAX and SHELLMAX waxes from Shell, synthetic waxes, low molecular weight polyethylene and polypropylene, and naturally occurring waxes. As a component of a hot melt packaging adhesive, wax may comprise up to about 50 percent by weight of the composition. As a barrier coating, wax may comprise up to about 95 percent by weight of the composition.
Various types of fillers and pigments may also be included in the formulations. This is especially true for exterior sealants in which fillers are added not only to create the desired visual appeal, but also to improve the weatherability of the sealant Suitable fillers include calcium carbonate, clays, talc, silica, zinc oxide, titanium dioxide and the like. The amount of filler added may range up to about 65 percent by weight of the composition, depending on the type of filler and the application for which the composition is intended.
Stabilizers may be added to protect the compositions against degradation due to heat, oxygen, ozone or ultraviolet (UV) light. Primary antioxidants include sterically hindered phenolics such as butylated hydroxy toluene. Secondary antioxidants such as phosphites, like tris-nonylphenyl phosphite, or thioethers may also be used. Various other stabilizers such as UV absorbers and hindered amine light stabilizers may be added to protect against UV degradation. The amount of stabilizer added is usually less than about 1 percent by weight However, for applications requiring very long durability, stabilizers may be added up to about 6 percent by weight.